Process for producing unsaponifiablesfree tall oil products

ABSTRACT

CRUDE SOAP SKIMMINGS, FROM THE KRAFT PLUP PROCESS, ARE UP-GRADED BY REMOVING CONTAINED UNSAPONIFIABLES, THIS IS DONE BY ADMIXING THE SKIMMINGS WITH WATER AND A DEEMULSIFYING ALCOHOL (E.G. METHANOL), CLARIFYING THE MIXTURE, AND CONTAINING THE CLARIFIED SOLUTION WITH A HYDROCARBON (E.G. HEPTANE) WHEREBY THE UNSAPONIFIABLES ARE EDTREATED INTO THE HYDROCARBO PHASE. THE COMPOSITION OF THE EXTRACTION FEED IS CONTROLLED TO ENSURE THAT SUBSTANTIALLY ALL THE UNSAPONIFIABLES ARE EXTRACTED WHILE ONLY A VERY SMALL AMOUNT OF THE SOAPS REPORT IN THE HYDROCARBON PHASE. THE RAFFINATE IS THEN DISTILLED TO RECOVER THE ALCOHOL.

A ril 9, 1914 PROCESS FOR PRODU Filed March 10, 1972 CLARIFICATIONSOLVENT ALCOHOL RECOVERY BY ALKALINE DISTILLATION 16 Sheets-Sheet 1SOAPS SKIMMINGS CON AINABLE UNSAPONIFIABLES HYDROCARBON CONTAININGSOLIDS AND SOME UNSAPON l FIAB LE5 EXTRACTION o CONTAINING ALLUNSAPONIFIABL REMAI MN 6 CLARIFIED SOAPS SOLUTION (SOAPS SKIMMINGSWATER+ALCOHOL+ UNSAPONIFIABLES) DE'EMULSIFYING ALCOHOL e. g. METHANOLe.q. h- HEP ANE TO EXTRACT SOME UNSAPONIFIA BLES AND REMOVE SOLIDSHYDROCARBON SOLVENT EXTRACTION CO LUMN UNSAPONIFIAB LES (COUNTERCURRENT) HYDROCARBON 0.0. h- HEPTANE CLARIFIED UNSAPONIFIABLES FREESOAPS SOLUTION (SOAPS SKIMMINGS WATER+ ALCOHOL) PRE- HEAT TO VAPORIZEFEED DISTILLATION COLUMN CLARIFIED, UNSAPONIF'IABLES FREE SOAPS SOLUTION(SOAPS SKIMMINGS+ WATER) April 9, 1974 L, MlTCHELL ET AL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS 16Sheets-Sheet 3 Filed March 10, 1972 HEPTANE MAN /\/\/W mum/ Av. FEED um;4/ vAv THANOL TER April 9, 1974 D, MlTCHELL ET AL 3,803,114

ALL 011,

PROCESS FOR PRODUCING JNSAPONIFIABLES-FREE T Filed March 10, 1972 wwwwwwI April 9, 1974 D. 1.. MITCHELL ETAL PROCESS FOR PRODUCINGUNSAPONIPIABLES -FRI1FL FALL ()II, PRODUCT? Filed March 10, 1972 l6Sheets-Sheet b April 9, 1974 MlTCHELL ET AL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL, OIL PRODUCTS FiledMarch 10, 1972 1G Sheets-Sheet 6 YAVA AYAY

AYAYAYA AYAVAYAVA AYAVAYAVAYA AYAYWA I FEED use Y PROCESS FOR PRODUCINGUNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed Maich 10, 1972 April D. 1..MITCHELL ETA!- 16 Sheets-Sheet April 9, 1974 D, MlTcHELL ET AL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed Harsh10, 1972 15 Sheets-Sheet 6 April 9, 1974 L, M|TCHELL E'TAL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed Hatch10, 1972 16 Sheets-Sheet J:-

AYAYAYA AVA AYAY

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FEED LINE METHANOL WATER A April 1974 D. L. MITCHELL ETAL PROCESS. FORPRODUCING UNSAPC-NIFIABLES-FREE TALL OIL PRODUCTS Filed March 10, 1972l6 Sheets-Sheet 10 zomm uomorx Q April 9, 1974 0. L. MITCHELL ET u.3,803,114

PROCESS FOR PRODUCING UNSAONlFIABLES-}-'REE TALL OIL PRODUCTS FiledMarch 10, 1972 16 Sheets-Sheet 11 FEED LINE METHANOL +WATER A April 9,1974 D. L. MITCHELL ET AL 3,803,114

PROCESS FOR YRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed March10, 1972 1,6 Sheets-Sheet 12 ,6 Weight Froc'ion Soups '0 Upper Phase vsHydrocarbon Concentration in System I I I I l I I I I I I I I lncubclmrManual Mixing Tumine Mixing I4 20% Solids in Stock Solufion 19% Solidsin Stock Solution 3 9 g I X o O I I I I I I I I I I I I I I 10 4O 10 2O30 4O 50 6O 96 Hydrocarbon in System A ril 9, 1974 rrc ET AL 3,803,114

PROCESS F R PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed March10, 1972 1G Sheets-Sheet 15 gJE-J- l l I l I l l l 1 I l I Ex'r cf PhaseComposi'ion (Turbine Mixing) \3 H 5 10 d 5 X l l l l l l l l l I l l 1 23 4 5 6 7 8 9 10 H 12 13 14 I5 I W? 96 Solids in Ex'mct Phase April 9,1974 L, MlTCHELL ETAL 3,803,114 PROCESS FOR PRODUCING UNSAPONIFIABLES-FRBE TALL OIL PRODUCTS Filed March 10, 1972 L6Sheets-Sheet 14 FI QJEE.

ExIrOCi Phase Composi'ion (Turbine Mixing I 2 3 4 8 9 I0 \1 l2 I3 14 WtUnsuponifiables in Extract Phase April 9, 1974 MlTCHELL ETAL 3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREJE TALL OIL PRODUCTS FiledMarch 10, 1972 16 Sheets-Sheet 15 I gJfi-l.

Exlrdd Phase Conposiflon (Equilibrium,

34% Stock Solids (Symbol o) 20% Stock Solids (Symba! o 20% Stock Solids(Symbol I) 41% smk Solids (Symbol O =-'-='1'- 20% Sum Solids (Symbol') ll l l l I l I l I l l l l I 2 3 4 5 6 7 8 9 I0 H I2 13 14 I5 WIUnsuponifiubles in Extract Phaso April 9, 1974 D. L. MITCHELL EI'AL3,803,114

PROCESS FOR PRODUCING UNSAPONIFIABLES-FREE TALL OIL PRODUCTS Filed March10, 1972 16 Sheets-Sheet l6 glf-E.

Y T I F T I' l l I l I l I I Extruc' Phase Composi'ion l3 (Equilibrium)34% Stock Solids (Symbol 0) 4 20% Stock Solids (Symbol Q 3 I l l l l J ll l l l l l l I 2 3 4 5 6 7 8 9 10 H 2 l3 H W! Solids in Extract Phasenited States Patent (3" US. Cl. 26097.7 1 Claim ABSTRACT OF THEDISCLOSURE Crude soap skimmings, from the Kraft pulp process, areupgraded by removing contained unsaponifiables. This is done by admixingthe skimmings with water and a deemulsifying alcohol (e.g. methanol),clarifying the mixture, and containing the clarified solution with ahydrocarbon (e.g. heptane) whereby the unsaponifiables are extractedinto the hydrocarbon phase. The composition of the extraction feed iscontrolled to ensure that substantially all the unsaponifiables areextracted while only a very small amount of the soaps report in thehydrocarbon phase. The rafiinate is then distilled to recover thealcohol.

BACKGROUND OF THE INVENTION This invention relates to a process forproducing upgraded soap solution from Kraft pulp process soap skimmings.The enriched solution contains fatty and resin acid soaps, but has hadthe normally present unsaponifiables content substantially removedduring processing. The product solution finds use as a high qualityfeed-stock from which crude and refined tall oil products can be made.

Soap skimmings are a by-product of the well known Kraft process. Thisprocess is used to produce wood pulp from woods which contain resinousconstituents known as wood extractives. Woods especially abundant inthese extractives are the various species of pine, balsam, cedar, larchand some species of spruce and hemlock.

The Kraft (or sulphate) process involves cooking wood chips. This isdone at elevated temperature and pressure in dilute alkaline liquorswhich contain sodium hydroxide and sodium sulphide as the activeingredients. Cooking efiects cellular breakdown and dissolution of thelignin, wood extractives and hemicelluloses. Additionally, it rendersthe cellulose in a dispersed, fibrous form which can be separated byfiltration. The spent cooking liquor (known as black liquor) isseparated and concentrated to a solids content suitable for combustionin a recovery furnace (about 60-70% soluble solids). Concentration iscarried out by passing the black liquor through a series ofmultiple-efiect evaporators. After several stages (30% soluble solidscontent), a portion of the solids, known as crude sulphate soaps,becomes insoluble. At this point, the black liquor is transferred to aholding tank and these soaps are skimmed oil? and recovered. Theskimmings consist of a mixture of solids material (50-70%) associatedwith an entrained liquid portion (30-50%).

.The soap skimmings when diluted with water give a product which usuallycomprises:

as solids:

suspended fibres insoluble sodium salts (organic and inorganic) somelignin in solution:

Water some lignin fatty and resin acid sodium soaps unsaponifiables odorbodies (such as 'mercaptans and disulphides) color bodies (principallysodium soaps of oxidized resin acids and oxidized unsaponifiables) ICCTypical soap skimmings from Alberta, Canada and North American westcoast mills would have the compositions given in Table 'I.

TABLE I [Composition of soap skimmings] Percent by weight Alberta Westcoast Constituent Sodium salts of fatty and resin acids Unsaponifiables10 15 Moisture and low molecular weight volatiles 35-40 37 Lignin,cellulose, inorganic salts 7-12 10 The soap skimmings are usuallytreated to produce crude tall oil; this product may be further refinedto produce the distilled fractions of tall oil.

The first step in this treatment involves reacting the skimmings withsulphuric acid. Hydrogen ions substitute for the sodium ions to convertthe soaps to fatty and resin acids. The products of acidulation separateinto three layers in a batch reactor. The top layer is referred to asthe crude tall oil layer. Its main constituents comprise fatty acids,resin acids, unsaponifiables and esters. Small amounts of suspendedsolids and water are also present in this layer. The second orintermediate layer is called the lignin layer. It contains the bulk ofthe lignin and insoluble non-soap solids which were originally presentin the skimmings. The bottom layer is mainly made up of sodium sulphateand water.

The crude tall oil is drawn off and can be sold as such or can befurther refined by fractional distillation. Typical compositions ofnorthern (made from woods grown in Canada and the northern UnitedStates) and southern (made from woods grown in the southern UnitedStates) crude tall oils are shown in Table IL TABLE II [Analysis andcharacteristics of northern and southern tall oils] Acid number -135-175 It will be noted that tall oils are characterized by their acidnumber. This is simply a quantitative measure of the concentration ofconstituents present in the oil that possess acidic groups. Morespecifically, it is the number of milligrams of KOH required toneutralize one gram of the oil.

The crude tall oil is a dark brown, viscous, opaque liquid possessing anoffensive odor. The dark color originates from traces of occluded blackliquir and oxidized resin acids. Insoluble inorganic salts and shortlengths of cellulose fibre product the opacity. (The Gardner Numberserves as an industry measure of the color qualities of the material.)Kraft sulphurous products, hydrogen sulphide, organic sulphides anddisulphides generate the unpleasant odor.

In this crude state, the applications of crude tall oil are limited touses where color and odor are not very important. In addition to thelimited applicability of the crude tall oils in general, northern crudetall oil suffers from an even greater disadvantage of applicabilitybecause of the proportionately higher unsaponifiables content; theseconstituents produce a plasticizing effect on certain formulations usingcrude tall oil.

For most applications, it is necessary to upgrade the crude tall oil.This is done by substantially eliminating color and odor bodies and alsoby separating the blend of acids into concentrated fractions of whichfatty and resin acids constitute the products of economic importance.Upgrading is normally done by distillation.

Distillation involves flashing the crude tall oil at 160- 260 C. and ata pressure of 1-10 mm. Hg. The volatile constituents are vaporized andleave behind a residue. The residue contains the occluded fibres,insoluble salts, suspended solids and lignin. In an idealizeddistillation, starting with a feed stock of low unsaponifiables content,the vapors would be fractionated into six product streams as follows:

(1) Gases (water, sulphides, disulphides);

(2) Heads (low molecular weight (C16) fatty acids and unsaponifiables);

(3) A main fatty acid fraction (C18 chain acids);

(4) A distilled tall oil fraction (C20 chain acids blended with some C20ring acids);

(5) A resin acid fraction (C20 ring acids); and

(6) Pitch, containing esters, sterols and polymerization products.

It should be noted that the prior art distillation is carried out underacidic conditions.

Through these operations, the bulk of the undesirable insolublesuspended solids present in the soap skimmings have been removed.Additional insoluble suspended solids generated by the acidulationprocess have been further removed during acidulation or during thesubsequent operation of flashing the crude tall oil prior to fractionaldistillation.

Returning again to Table II, it will be seen that the main dilference,in terms of chemical composition, between the northern and southerncrude tall oils is the amount of contained unsaponifiables. It isapparent that the extent of unsaponifiables content is governed by thespecies and geographic origin of the wood involved.

Unsaponifiables can be generally described as a class of organiccompounds which do not contain a saponifiable group (such as carboxyl,thiolate or sulphonate). More specifically, FIG. 2 shows a breakdown ofthe unsaponifiables contained in a typical Alberta soap skimmings. Thesecompounds can be divided into three general groups:

(1) High molecular weight alcohols such as diterpene (C20) alcohols,linear (C20-C26) alcohols and sterols;

(2) Diterpene aldehydes and ketones; and

(3) Hhydrocarbons and triterpenes.

It will be noted that approximately As of the unsaponifiables are madeup of a complex combination of alcohols.

In comparison, tall oils originating from the southern United Statesdiffer in their unsaponifiables constituent composition both in kind anddegree. Their major unsaponifiable constituents are the sterols andhydrocarbons; diterpene alcohols and diterpene aldehydes and ketones arenot present as major constituents. The substantially decreased contentof diterpene alcohols, aldehydes and ketones results in considerablydifferent distillation characteristics and distillation products.

The presence of unsaponifiables is undesirable in both crude and refinedtall oil products. This is particularly a problem when large amounts ofunsaponifiables are present, as in the case of northern feeds. In thecase of crude, tall oil, unsaponifiables dilute the acid contentresulting in products of low acid number. In the case of using northerncrude tall oils for distillation feed-stock, various problems result inthe distillation step and in the color quality and acid number of thedistilled products. These characteristics may affect the marketabilityof northern crude tall oil destined for distillation feed-stock.

The tall oil industry has adapted itself to getting along with productshaving small amounts of unsaponifiables; however, it penalizes orrefuses to use high unsaponifiables content products such as areobtained from northern woods.

The following examples will illustrate the difficulties in usingnorthern crude tall oil either as a crude product or as a feed-stock fora distillation operation.

In limited operations, crude tall oil may be used as an ingredient ininexpensive, low quality paint, particularly where dark colored productsare not considered a disadvantage. Such formulations are usually basedon the acid number or acid content of the crude tall oil. It is commonfor paint manufacturers to require crude tall oil having an acid numbergreater than a typical northern crude tall oil will only have an acidnumber of about 130.

The major proportion of available crude tall oil is utilized insubsequent refining processes of which fractional distillation is themost important and the most common. Northern crude tall oils areconsidered poor feed-stocks for such refining operations because oftheir contained unsaponifiables constituents. These tall oils haveunsatisfactory distillation yields and the quality of the distillates isinferior to that produced by southern tall oils, particularly withrespect to unsaponifiables content in distillants. These disadvantagescome about in two ways. Firstly, the acids and hydroxyl containingunsaponifiables (alcohols) react with each other, particularly atelevated temperatures, to form esters. Most of these esters havesufiiciently high molecular weights to be non-volatile and report in thepitch fraction during distillation and are subsequently lost. The acidcontent of the esters is also, of course, lost. Secondly, duringdistillation of northern tall oils the more volatile unsaponifiablescompounds tend to be carried over with the acid fraction because thevapor pressures of the diterpene alcohols and aldehydes are very closeto those of the fatty acids and resin acids. In this respect, thedistillation characteristics differ from the southern tall oils. As aresult, the volatile diterpene alcohols and aldehydes dilute orcontaminate the separate acid streams, thus defeating, to some extent,the purpose of the distillation. Since ester formation is timedependent, the distiller could increase the distillation temperature andfeed rate through the tower to reduce the esterification. However, indoing so, he will increase the carry-over of volatile unsaponifiablesinto the acid fractions. Consequently the distilled products will besubstantially contaminated with non-acid constituents which may penalizethe value of the products.

These problems facing the distiller are so serious that many northerncrude tall oils cannot be fractionated on a paying basis because of theyields obtained and also because of the quality of the distillationproducts derived.

To sum up the foregoing, a northern pulp manufacturer produces a soapskimmings product which has an undesirably high unsaponifiables content.He suffers penalties if he sells the product in crude tall oil form. Hefinds that the fractionation procedures, which were originally developedfor southern-type materials, are not usually applicable to his product.

One answer to all of these problems would be to remove theunsaponifiables from the soap skimmings.

Unsaponifiables have hydrophobic properties and are soluble in certainorganic solvents. It had long been suspected that low molecular weighthydrocarbons, such as hexane and heptane, could be used to extract themfrom aqueous solutions. The unsaponifiables are preferentially solublein the hydrocarbons and they, in turn, are substantially immiscible inthe soap solution. However, there was a serious problem which preventeduseful application of this knowledge. When the aqueous soap solution andthe hydrocarbon were mixed together, they would form a very stableemulsion.

The problem of emulsification was solved by Christenson and Gloyer.Their solution was described in US. Pat. No. 2,530,809. Basically, theytaught that certain alcohols would act as de-emulsifiers if provided ina water-soap skimmings-hydrocarbon system. They also taught operativeranges of composition which, if observed, would result in rapid phaseseparation. In other words, if water, soap skimmings, alcohol andhydrocarbon were shaken up together, the unsaponifiables would beextracted by the hydrocarbon and, when the mixture was allowed to stand,the components would quickly separate into a lower phase, consistingmainly of soap-water-alcohol, and an upper phase consisting mainly ofhydrocarbon and unsaponifiables. They further taught that the quantitiesof sodium soaps which did become dissolved in the upper phase could beremoved by a subsequent operation of washing with water.

The process taught by Christenson and Gloyer was directed to therecovery of unsaponifiables as a source of sterols, useful in the drugindustry. Although the patentees recognized that the removal ofunsaponifiables would enhance acid yields from soap skimmings, they didnot teach an industrially operative process for accom' plishing thisend.

The present invention is a process.

SUMMARY OF THE INVENTION directed to providing such It is an object ofthis invention to provide a process for removing substantially all ofthe unsaponifiables and insoluble, non-soap solids from soap skimmingsto produce a purified soap solution. The product solution should be ahigh quality feed-stock. Crude tall oil and distilled products made fromit should be substantially free of unsaponifiables and should becharacterized by high acid numbers and improved color characteristics.

It is another object to provide a process, the practice of which willresult in improved yields of fatty and resin acids, in the form ofdistillation products, from soap skimmings.

It is another object to provide a soaps upgrading process, involvingsolvent extraction of unsaponifiables and alcohol recovery, which iscarried out under alkaline conditions.

It is another object to provide a soaps upgrading process involvingsolvent extraction of unsaponifiables wherein washing of the extractfraction to recover dissolved soaps is not necessary.

It is another object to provide a soaps upgrading process, involvingseparation of suspended solids and sterols, wherein the solids andsterols are recovered in the form of a filter cake. This cake forms apreferable feedstock for the production of phytosterols.

It is another object to provide a soaps upgrading process involvingseparation of undissolved solids wherein these solids are recovered as ahydrocarbon-wetted fioc under two phase formation which minimizesemulsion formation and recovers an extractable portion in undegradedform.

It is another object to provide a soaps upgrading process, involvingalcohol recovery by distillation, which is conducted in a manner toavoid foaming, fouling and plugging in the distillation column.

These and other objects of the invention will be apparent fromconsideration of the following specification and appended drawings.

'In accordance with the invention, the following steps and limitationsare employed:

Firstly, crude soap skimmings are admixed with water and ade-emulsifying alcohol to form a mixture comprising a soap solution,dissolved unsaponifiables and undissolved solids.

Secondly, the mixture is preferably treated to remove substantially allits undissolved solids. This may be done by mixing the mixture withhydrocarbon and allowing the product to settle to form an upperhydrocarbon phase and a lower soap solution phase. The undissolvedsolids report in the hydrocarbon phase as a hydrocarbon-wetted fioclayer. This phase can be drawn off to leave a clarified soap solution.

Thirdly, the clarified soap solution is contacted with sufiicienthydrocarbon to extract substantially all the unsaponifiables presenttherein.

Suitable alcohols and hydrocarbons are known from the prior art. We havefound methanol, ethanol, n-propanol and isopropanol and mixtures thereofparticularly suitable as the de-emulsifying alcohol. Methanol ispreferred. Hexane, heptane and petroleum cuts containing one or both ofthem as major constituents are particularly suitable for use as thehydrocarbon solvent. 'Heptane is preferred. These hydrocarbons aresolvents for the unsaponifiables, are stable in alkaline conditions andare substantially immiscible in the soap solution.

The composition of the soap solution fed into the extraction vessel, theextent of dilution therein with hydrocarbon and the composition of thedistillation feed will preferably be controlled by the followinglimitations:

(a) Two phase separation of the soap solution and hydrocarbon must takeplace relatively quickly. This can be tested by placing a representativemixture in a laboratory separation funnel, shaking it manually for 10minutes and allowing it to stand. If substantially complete separationoccurs within 6 minutes the composition meets this requirement. UJS.Pat. No. 2,530,809 teaches systems in accordance with this requirement;

(b) The dissolved solids content in the extraction feed should berestricted to minimize retention of unsaponifiables in the rafiinatephase. In other words, dissolved solids content should be less than apredetermined maximum amount. This maximum amount is that amount whichwill result in a raffinate having an exhaustively extracted acid numberof 174, as arrived at by the following test:

Dilute a sample of the feed with hydrocarbon in the proportion which isto be used in the process; shake this mixture in a laboratory separationfunnel to reach a single stage equilibration; draw olf the hydrocarbonphase; repeat the procedure to take a total of six cross-currentextractions. If the acid number of the raffinate phase is equal to orgreater than about 174, then the dissolved solids content in theclarified soap solution is equal to or less than the preferred maximumpermissible amount;

(0) The extraction feed composition and hydrocarbon dilution should beselected to ensure that the extract stream from the decanter and/orextraction vessel contains less than about 5.5% by weight dissolvedsolids;

(d) The ratio of dry, unsaponifiables-free solids to Water in the feedto the distillation tower should be greater than about 3:7 so as to helpprevent uncontrollable foam ing therein.

Fourthly, the rafiinate is distilled, preferably under alkalineconditions, to recover alcohol. The end product soap solution issubstantially free of unsaponifiables and undissolved solids. Itcomprises a high quality feed-stock which may be acidulated to makesuperior crude tall oil.

Now, a number of the foregoing features require amplification:

Clarification of the soap solution prior to solvent extraction isimportant to the process. If the undissolved solids are not removed,plugging and fouling of the extraction tower, alcohol recovery tower andheat exchangers will occur. Additionally, clarification aids subsequentacidulation by removing a portion of the solids which would appear atthe intermediate acidulation layer.

Exercising control-of the dissolved solids in the extraction feed is apreferred feature. We have found that a high solids content results inlarge amounts of unsaponifiables being retained in the rafiinate. Byrestricting solids content, a raffinate can be produced which, whenacidulated, will have a desirable acid number (such as 174 or greater).The raffinate should have an acid number greater than about 174,otherwise the process is impractical.

Exercising control of the amount of solids dissolved in the extractphase is another preferred feature. This is done by carefully choosingthe extraction feed composition. If the solids content in the extractphase is kept below about 5.5 percent by weight, dissolution of soaps inthat phase is kept to a negligible amount. If the solids content isallowed to exceed 5.5%, substantial dissolution of soaps in that phasewill begin to take place. As a result, soap recoveries will decrease.Reclaiming of the lost soaps from the extract phase may then become anundesirable necessity.

Alkaline distillation of the clarified soap solution to recover alcoholis another preferred feature. We have found that foaming, which is themain stumbling block to distilling a soap solution, can be operativelycontrolled in a simple fashion. This is done by maintaining a minimumdry, unsaponifiables-free solids to water ratio in the feed to thedistillation tower and by minimizing vapor velocities in the strippingsection by pre-concentrating the distillation feed. These antifoamingmeasures are preferred features of the process.

Distillation is preferably carried out under alkaline conditions toavoid secondary recovery problems. If the soap solution is acidulatedbefore alcohol recovery, dissolved lignins in the system becomeinsoluble. These lignins cause serious fouling problems in the alcoholrecovery tower and associated heat exchangers. The undissolved ligninwould, therefore, have to be removed from the system beforedistillation. This lignin contains en trapped tall oil, alcohol andhydrocarbon. It would be necessary to salvage these by secondaryrecovery. In addition, noxious gases such as H 8, CO and mercaptanswould be generated during acidulation. They may also appear in thedistillation column. These gases are corrosive and may require use ofspecial construction materials. Additionally, they have to be ventedfrom the acidulation and distillation column. This results in aconcomitant loss of alcohol and hydrocarbon which may have to bereclaimed by secondary recovery.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a flow diagram of the process;

FIG. 2 is a schematic representation of the constituents which makeupthe unsaponifiables in an Alberta soap skimmings;

FIG. 3 is a triangular coordinate phase diagram based on the data ofTable 3A;

FIG. 4 is a triangular coordinate phase diagram based on the data ofTable 4A;

FIG. 5 is a triangular coordinate phase diagram based on the data ofTable 5A;

FIG. 6 is a triangular coordinate phase diagram based on the data ofTable 6A;

FIG. 7 is a triangular coordinate phase diagram based on the data ofTable 7A;

FIG. 8 is a triangular coordinate phase diagram based on the data ofTable 8A;

FIG. 9 is a triangular coordinate phase diagram based on the data ofTable 9A;

FIG. 10 is a triangular coordinate phase diagram based on the data ofTable 10A;

FIG. 11 is a triangular coordinate phase diagram based on the data ofTable 11A;

FIG. 12 is a plot showing the changes in amount of soaps which go to theupper phase during extractions with varying amounts of hydrocarbon.Three hydrocarbons were used: heptane (-x-xcurve), ISO-200 F. refineryfraction (O-. curve), and 190-210 F. refinery fraction (-I curve). Highshear mixing was used;

FIG. 12 -1 plots percent solids in the extract phase against the weightratio of the unsaponifiables in the extract phase and the soap in theextract phase;

FIG. 12-2 is the same as FIG. 12-1 except that percent unsaponifiablesin the extract phase is plotted. All the FIG. 12 curves are based on thedata of Table 12A;

FIGS. 13, 13-1 and 13-2 are similar to FIGS. 12, 12-1 and 12-2 exceptthat manual mixing was used. These figures are based on the data ofTables 13A, 13B and 13C.

8 DESCRIPTION OF THE PREFERRED EMBODIMENT The above mentionedlimitations can be best under stood and justified using triangular phasediagrams.

In our phase diagrams, we have plotted alcohol plus water, hydrocarbonand dry total solids. The semi-circular curve on each diagram dividesthe system into those compositions which would exist as a single phase(above the curve) from those compositions which would separate into twophases (beneath the curve). The curves have been developed byequilibrating a sample of a particular composition in a separatoryfunnel. The mixture was allowed to stand for 30 minutes and the extractand rafiinate phases were subsequently analyzed. The compositions of therafiinate phases were plotted to provide the left hand side of the phasecurve while the compositions of the extract phases were plotted todevelop the right hand side. The line joining the rafiinate, mixture andextract composition points is referred to as a tieline.

In FIG. 10, point D represents a composition of solids, hydrocarbon andaqueous alcohol phases in the mixture. This mixture separates into thetwo phases identified as points I and I on the phase diagram curve. Atie-line joins points I, D and I. The compositions of the two phasesgiven by I and J represents the equilibrium composition of the two phasemixture. For example, if a system represented by point D contains 14%dry solids, 36% methanol-water and 50% by weight hydrocarbon, then thecomposition of the rafiinate phase would be expressed as that given bypoint I on the phase diagram. This composition is solids 23%,methanol-water 67% and hydrocarbon 10%. The composition of the extractphase is given by point I on the phase diagram. This point has thefollowing composition: solids 4%, methanol-water 1.5% and hydrocarbon94.5%.

Not all compositions described under the phase diagram curve will givedesirable systems for our process. As mentioned, systems which do notcontain sufficient solids in the rafiinate phase have a tendency to foamduring subsequent alcohol recovery. Therefore a certain minimum solidscontent is desirable for operation of the alcohol recovery tower. Also,solids content in the system has a bearing on the degree to which theunsaponifiables are extracted during a multi-stage extraction operation.It has been found that systems containing a high solids content giveextracted soaps which still contain some unsaponifiables. These soaps,upon acidulation. give undesirably low acid numbers. Turning now to theextract phase, we have also found that soap losses to that phase dependupon the percentage solids dissolved in it. Soap losses through solutioninto the extract phase are kept to a minimum when the solids content ofthe extract phase is kept below 5.5% by weight.

FIG. 10 has two portions of the curve darkened in with a thick, blackline.

In accordance with the invention, in order to meet the requirements ofthe over-all process, any system (that 1s, composition of soaps,alcohol-water and hydrocar- 'bon), when shaken in a separatory funnel toreach single stage equilibration, should have a tie-line whose ends liein those portions of the curve described by the thick black lines. Inother words, the composition of the raffinate phase, after single stageequilibrium, should be defined by any composition given by the thickblack segment on the left hand portion of the diagram. Similarly, thecomposition of the extract phase, after single stage equilibrium, shouldbe described by a composition given by the thick black line appearing atthe right hand side of the diagram. All other tie lines that intersectthe phase diagram at locations other than those given by the thick blacklines will not give the preferred operating characteristics in theoverall process.

